<template>
    <ul class='list' >
        <li class='item' v-for='item of letters' :key='item' :ref='item'
        @click='handleLetterClick' @touchstart='handleTouchStart'
        @touchmove='handleTouchMove'
        @touchend='handleTouchEnd'
        >{{item}}</li>
    </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities: Object
    },
    computed:{
        letters () {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus: 0,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = 1
        },
        handleTouchMove (e) {
            if (this.touchStatus) {
                if (this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                const touchY = e.touches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
                if (index >= 0 && index < this.letters.length){
                    this.$emit('change', this.letters[index])
                }
                } ,16)
                
            }
        },
        handleTouchEnd () {
            this.touchStatus = 0
        }
    }
}
</script>

<style lang='stylus' scoped>
    @import '~styles/varibles.styl'
    .list
        display :flex
        flex-direction :column
        justify-content:center
        position : absolute
        top: 1.58rem
        right :0
        bottom :0
        width :.4rem
        .item
            line-height :.4rem
            text-align :center
            color : $bgColor
</style>
